This patent relates to a body implant which softens and/or swells when implanted in the body, a novel composition useful in preparing said implant and a method of preparing said implant. It further relates to methods of inserting a softening and/or swelling catheter or cannula into a blood vessel of an animal.
Body implants, in particular tubular implants inserted into the body such as catheters, cannulae, endotracheal tubes or the like need to be relatively stiff for ease of insertion in the body. Commercially available cannulae, for example, are typically made of fluorinated ethylenepropylene copolymer, polytetrafluoroethylene, poly(chlorotrifluoroethylene), or the like. When such commercial cannulae or catheters of such materials are left in the body for relatively long periods of time, trauma to the surrounding tissue may result.
Various compositions which soften in contact with water are known and some have been suggested for use as body implants. The following are illustrative.
U.S. Pat. No. 3,822,238, Blair et al, discloses water absorptive polyurethane polymers prepared from resins having a low ratio of carbon to oxygen to nitrogen or having ionic quaternary ammonium or salt groups in the resin backbone and a low amount of isocyanate. It is suggested that the polymers can be used as coatings or membranes or shaped by casting or machining to make body implants. There is no suggestion as to which polymers of the many disclosed would be useful for forming body implants. Nor is there any indication of what properties polymers for use as body implants should have.
U.S. Pat. No. 3,975,350, Hodgin et al, discloses hydrophilic crosslinked polyurethane systems useful as carrier systems for slow release of medication, as coatings or for body implants, such as catheters and cannulae. Again there is no suggestion as to which polyurethane systems would be useful for body implants.
U.S. Pat. No. 4,279,795, Yamashita et al, relates to materials capable of forming a hydrogel and having improved anti-thrombogenic properties. The polymer is a graft copolymer having a hydrophilic polymer backbone, e.g. a polymethacrylate, with hydrophobic moieties, e.g. polystyrene, grafted onto it. The hydrogel is said to be self-reinforcing and capable of being shaped into a tube, film, rod, etc.
U.S. Pat. No. 4,371,686, Yamamoto et al, discloses implanting into jugular and femoral veins of animals, tubes of a polyurethane containing polyoxyethylene and polyoxypropylene blocks. The polymers are said to be highly elastic and to possess anti-thrombogenic properties.
U.S. Pat. No. 4,439,583, Gould et al, discloses a polyurethane diacrylate composition which forms a hydrogel on immersion in water. The compositions are said to have a variety of uses including use in body implants such as catheters and cannulae.
U.S. Pat. No. 4,454,309, Gould et al, discloses a composition comprising a hydrophilic polyurethane resin and a polyene selected from polyalkyl esters and polyacrylic acid esters. The compositions are said to have a variety of uses including use in body implants such as catheters and cannulae.
U.K. Pat. No. 1,511,563, Ciba-Giegy AG, relates to water-insoluble hydrophilic copolymers, preferably a methacrylate copolymer. The copolymers are primarily useful as drug delivery systems. It is disclosed that the copolymers can be fashioned into substitute blood vessels or extracorporeal shunts.
Japanese Kokai Sho 52-9087 to Nakashima et al, discloses block and or graft copolymers made of hydrophilic polymer segments and hydrophobic polymer segments and having a phase-separated microstructure with one of the segments, preferably the hydrophilic, forming a continuous phase and the other a dispersed phase. The copolymers are said to have good anti-thrombogenic properties. The copolymers are said to be useful for medical and therapeutic equipment that may come into contact with blood, such as, for example, vascular catheters, cannulae, shunts, etc.
In summary, while a great number of compositions are disclosed in each of these patents, there is no indication of which particular compositions would be suitable for use as a body implant, such as a catheter or cannula. Where a particular composition has been made into a catheter or cannula, the composition selected is one which does not provide a body implant having desired properties.
It has now been discovered that a body implant having desirable properties can be made from a novel multiple phase polymeric composition having a non-hydrophilic phase and hydrophilic phase, the relative amounts of the non-hydrophilic and hydrophilic components being adjusted, depending on the particular materials employed, to provide a composition having certain properties. The body implant and the composition from which it is made softens and/or swells when in the body and is sufficiently soft when in the body to reduce trauma to the surrounding tissue. Swelling of the implant permits insertion of a smaller device and/or can result in pressure around a wound site reducing bleeding and bacterial invasion into the wound. The implant is sufficiently strong and tough when in the body to maintain its desired shape, to resist deformation and to be capable of removal without tearing and leaving any undesired fragments in the body. For certain applications, the implant has a high initial stiffness for insertion yet softens when in the body to become pliable.